Lubricating oil composition and methods for controlling foam tendency and/or foam stability

ABSTRACT

Provided is a lubricating oil composition and methods for controlling one or more of foam tendency and foam stability in such composition using as the oil a mixture of at least two base stocks. The at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. When the surface tension difference between them is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. Two low-foaming base stocks can produce a significant high foam response that reduces or eliminates the need for pro-foaming additives.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/838,669, filed on Apr. 25, 2019, the entire contents of which are incorporated herein by reference.

FIELD

This disclosure relates to lubricating oil compositions and methods for controlling, e.g., enhancing or reducing, foam tendency and/or foam stability in such lubricating oil compositions.

BACKGROUND

Lubricants in commercial use today are prepared from a variety of natural and synthetic base stocks admixed with various additive packages and solvents depending upon their intended application. The base stocks typically include mineral oils, poly alpha olefins (PAO), gas-to-liquid base oils (GTL), silicone oils, phosphate esters, diesters, polyol esters, alkylated aromatics, polyalkylene glycols and the like.

Lubricating oils often contain defoamants to inhibit foam formation. However, there are many applications where a foaming lubricant is desirable. In these situations air bubbles provide acoustic suppression, ease of application and block particulate contaminants from entering machinery. Foam is particularly beneficial in delivering lubricants to difficult-to-reach areas (e.g., inside of chain link galleyways) and aerosol cans containing pro-foaming lubricant are commercially available.

Currently, pro-foaming additives are used to induce foam in otherwise low-foaming base stocks. However, pro-foaming additives are costly, cause extra complexity in blending and can limit the compatibility of the lubricant.

There is a need for foaming lubricants that do not require pro-foaming additives. It would be highly desirable to provide foaming lubricants without the need for pro-foaming additives that are costly, cause extra complexity in blending and can limit the compatibility of the lubricant.

The present disclosure also provides many additional advantages, which shall become apparent as described below.

SUMMARY

This disclosure is directed in part to a method for controlling one or more of foam tendency and foam stability in a lubricating oil comprising providing as the lubricating oil a mixture of at least two base stocks. The at least two base stocks have a surface tension difference between them as measured by the Wilhelmy Plate method such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. When the surface tension difference between them is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

This disclosure relates in part to a lubricating oil comprising a mixture of at least two base stocks. The at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture. When the surface tension difference between them is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

In this disclosure, it has been found that two low-foaming base stocks can produce a significant high foam response that reduces or eliminates the need for pro-foaming additives. The at least two base stocks have a surface tension difference between them of greater than 1.0 dynes/cm. Alternatively, foam can be reduced or eliminated by blending base stocks with a surface tension difference between them of less than 1.0 dynes/cm. The foaming property is derived from the interactions between the base stocks when they are combined in an appropriate ratio. As the mixture contains only unadditized hydrocarbon base stocks, this disclosure has significant implications for lubricant development.

In accordance with this disclosure, the foaming response can be controlled by selecting base stocks with appropriate surface tension difference, i.e., a surface tension difference between them of greater than 1.0 dynes/cm for enhancing the foaming response and a surface tension difference between them of less than 1.0 dynes/cm for reducing the foaming response. Lubricating oils in accordance with this disclosure can exhibit enhanced or reduced (e.g., eliminated) foam tendency and/or foam stability.

Further objects, features and advantages of the present disclosure will be understood by reference to the following drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, wherein:

FIG. 1 graphically depicts mixtures of two different PAOs that produce a foam tendency increase when combined in an appropriate ratio.

FIG. 2 graphically depicts the difference in surface tension versus LOAST volume increase at 25% treat rate of several different base stocks that all have a kinematic viscosity of approximately 6 cSt at 100° C.

FIG. 3 graphically depicts the foaming tendency of PAO-A and PAO-B as a function of the wt. % of Group V alkylated aromatic added to the blend.

FIG. 4 depicts in tabular form the foaming tendency of 3-component base stock blends which include 2 different PAO's and and a PAG co-basestock.

DETAILED DESCRIPTION Definitions

“About” or “approximately.” All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.

“Major amount” as it relates to components included within the lubricating oils of the specification and the claims means greater than or equal to 50 wt. %, or greater than or equal to 60 wt. %, or greater than or equal to 70 wt. %, or greater than or equal to 80 wt. %, or greater than or equal to 90 wt. % based on the total weight of the lubricating oil.

“Minor amount” as it relates to components included within the lubricating oils of the specification and the claims means less than 50 wt. %, or less than or equal to 40 wt. %, or less than or equal to 30 wt. %, or greater than or equal to 20 wt. %, or less than or equal to 10 wt. %, or less than or equal to 5 wt. %, or less than or equal to 2 wt. %, or less than or equal to 1 wt. %, based on the total weight of the lubricating oil.

“Essentially free” as it relates to components included within the lubricating oils of the specification and the claims means that the particular component is at 0 weight % within the lubricating oil, or alternatively is at impurity type levels within the lubricating oil (less than 100 ppm, or less than 20 ppm, or less than 10 ppm, or less than 1 ppm).

“Other lubricating oil additives” as used in the specification and the claims means other lubricating oil additives that are not specifically recited in the particular section of the specification or the claims. For example, other lubricating oil additives may include, but are not limited to, antioxidants, detergents, dispersants, antiwear additives, corrosion inhibitors, viscosity modifiers, metal passivators, pour point depressants, seal compatibility agents, antifoam agents, extreme pressure agents, friction modifiers and combinations thereof.

“Other mechanical component” as used in the specification and the claims means an electric vehicle component, a hybrid vehicle component, a power train, a driveline, a transmission, a gear, a gear train, a gear set, a compressor, a pump, a hydraulic system, a bearing, a bushing, a turbine, a piston, a piston ring, a cylinder liner, a cylinder, a cam, a tappet, a lifter, a gear, a valve, or a bearing including a journal, a roller, a tapered, a needle, and a ball bearing.

“Hydrocarbon” refers to a compound consisting of carbon atoms and hydrogen atoms.

“Alkane” refers to a hydrocarbon that is completely saturated. An alkane can be linear, branched, cyclic, or substituted cyclic.

“Olefin” refers to a non-aromatic hydrocarbon comprising one or more carbon-carbon double bond in the molecular structure thereof.

“Mono-olefin” refers to an olefin comprising a single carbon-carbon double bond.

“Cn” group or compound refers to a group or a compound comprising carbon atoms at total number thereof of n. Thus, “Cm-Cn” group or compound refers to a group or compound comprising carbon atoms at a total number thereof in the range from m to n. Thus, a C1-C50 alkyl group refers to an alkyl group comprising carbon atoms at a total number thereof in the range from 1 to 50.

“Carbon backbone” refers to the longest straight carbon chain in the molecule of the compound or the group in question. “Branch” refer to any substituted or unsubstituted hydrocarbyl group connected to the carbon backbone. A carbon atom on the carbon backbone connected to a branch is called a “branched carbon.”

“Epsilon-carbon” in a branched alkane refers to a carbon atom in its carbon backbone that is (i) connected to two hydrogen atoms and two carbon atoms and (ii) connected to a branched carbon via at least four (4) methylene (CH₂) groups. Quantity of epsilon carbon atoms in terms of mole percentage thereof in a alkane material based on the total moles of carbon atoms can be determined by using, e.g., ¹³C NMR.

“Alpha-carbon” in a branched alkane refers to a carbon atom in its carbon backbone that is with a methyl end with no branch on the first 4 carbons. It is also measured in mole percentage using ¹³C NMR.

“T/P methyl” in a branched alkane refers to a methyl end and a methyl in the 2 position. It is also measured in mole percentage using ¹³C NMR.

“P-methyl” in a branched alkane refers to a methyl branch anywhere on the chain, except in the 2 position. It is also measured in mole percentage using ¹³C NMR.

“SAE” refers to SAE International, formerly known as Society of Automotive Engineers, which is a professional organization that sets standards for internal combustion engine lubricating oils.

“SAE J300” refers to the viscosity grade classification system of engine lubricating oils established by SAE, which defines the limits of the classifications in rheological terms only.

“Base stock” or “base oil” interchangeably refers to an oil that can be used as a component of lubricating oils, heat transfer oils, hydraulic oils, grease products, and the like.

“Lubricating oil” or “lubricant” interchangeably refers to a substance that can be introduced between two or more surfaces to reduce the level of friction between two adjacent surfaces moving relative to each other. A lubricant base stock is a material, typically a fluid at various levels of viscosity at the operating temperature of the lubricant, used to formulate a lubricant by admixing with other components. Non-limiting examples of base stocks suitable in lubricants include API Group I, Group II, Group III, Group IV, and Group V base stocks. PAOs, particularly hydrogenated PAOs, have recently found wide use in lubricants as a Group IV base stock, and are particularly preferred. If one base stock is designated as a primary base stock in the lubricant, additional base stocks may be called a co-base stock.

All kinematic viscosity values in this disclosure are as determined pursuant to ASTM D445. Kinematic viscosity at 100° C. is reported herein as KV100, and kinematic viscosity at 40° C. is reported herein as KV40. Unit of all KV100 and KV40 values herein is cSt unless otherwise specified. When describing the kinematic viscosity at 100° C. is “essentially” maintained, the kinematic viscosity at 100° C. is expected to vary less than 0.2 cSt as measured by ASTM D445.

All viscosity index (“VI”) values in this disclosure are as determined pursuant to ASTM D2270.

All Noack volatility (“NV”) values in this disclosure are as determined pursuant to ASTM D5800 unless specified otherwise. Unit of all NV values is wt %, unless otherwise specified.

All pour point values in this disclosure are as determined pursuant to ASTM D5950 or D97.

All CCS viscosity (“CCSV”) values in this disclosure are as determined pursuant to ASTM 5293. Unit of all CCSV values herein is millipascal second (mPa·s), which is equivalent to centipoise), unless specified otherwise. All CCSV values are measured at a temperature of interest to the lubricating oil formulation or oil composition in question. Thus, for the purpose of designing and fabricating engine oil formulations, the temperature of interest is the temperature at which the SAE J300 imposes a minimal CCSV.

All percentages in describing chemical compositions herein are by weight unless specified otherwise. “Wt. %” means percent by weight.

Lubricating Oils and Methods of this Disclosure

As indicated above, this disclosure provides that two low-foaming base stocks can produce a significant high foam response that reduces or eliminates the need for pro-foaming additives. The foaming property is derived from the interactions between the base stocks when they are combined in an appropriate ratio. As the mixture contains only unadditized hydrocarbon base stocks, this disclosure has significant implications for lubricant development.

In one form of this disclosure, provided is a lubricating oil comprising a mixture of at least two base stocks, wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

In another form of this disclosure, provided is a method for controlling one or more of foam tendency and foam stability in a lubricating oil comprising providing as the lubricating oil a mixture of at least two base stocks; wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

Alternatively, the at least two base stocks of the lubricating oil and the methods have a surface tension difference between them such that, when the surface tension difference is greater than 1.2 dynes/cm, or greater than 1.4 dynes/cm, or greater than 1.6 dynes/cm, or greater than 1.8 dynes/cm, or greater than 2.0 dynes/cm, or greater than 2.2 dynes/cm, or greater than 2.4 dynes/cm, or greater than 2.6 dynes/cm, or greater than 2.8 dynes/cm, or greater than 3.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

Alternatively, the at least two base stocks of the lubricating oil and the methods have a surface tension difference between them such that, when the surface tension difference is less than 0.8 dynes/cm, or less than 0.6 dynes/cm, or less than 0.4 dynes/cm, or less than 0.2 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

Lubricating Oil Base Stocks

A wide range of lubricating oils is known in the art. Lubricating oils that are useful in the present disclosure are both natural oils and synthetic oils. Natural and synthetic oils (or mixtures thereof) can be used unrefined, refined, or rerefined (the latter is also known as reclaimed or reprocessed oil). Unrefined oils are those obtained directly from a natural or synthetic source and used without additional purification. These include shale oil obtained directly from refining operations, petroleum oil obtained directly from primary distillation, and ester oil obtained directly from an esterification process. Refined oils are similar to the oils discussed for unrefined oils except refined oils are subjected to one or more purification steps to improve the at least one lubricating oil property. One skilled in the art is familiar with many purification processes. These processes include solvent extraction, secondary distillation, acid extraction, base extraction, filtration, and percolation. Rerefined oils are obtained by processes analogous to refined oils but using an oil that has been previously used as a feed stock.

Groups I, II, III, IV and V are broad categories of base oil stocks developed and defined by the American Petroleum Institute (API Publication 1509; www.API.org) to create guidelines for lubricant base oils. Group I base stocks generally have a viscosity index of between 80 to 120 and contain greater than 0.03% sulfur and less than 90% saturates. Group II base stocks generally have a viscosity index of between 80 to 120, and contain less than or equal to 0.03% sulfur and greater than or equal to 90% saturates. Group III stock generally has a viscosity index greater than 120 and contains less than or equal to 0.03% sulfur and greater than 90% saturates. Group IV includes polyalphaolefins (PAO). Group V base stocks include base stocks not included in Groups I-IV. The table below summarizes properties of each of these five groups.

Base Oil Properties Saturates Sulfur Viscosity Index Group I <90 and/or >0.03% and ≥80 and <120 Group II ≥90 and ≤0.03% and ≥80 and <120 Group III ≥90 and ≤0.03% and ≥120 Group IV Includes polyalphaoefins (PAO) Group V All other base oil stocks not included in Groups I, II, III or IV

Natural oils include animal oils, vegetable oils (castor oil and lard oil, for example), and mineral oils. Animal and vegetable oils possessing favorable thermal oxidative stability can be used. Of the natural oils, mineral oils are preferred. Mineral oils vary widely as to their crude source, for example, as to whether they are paraffinic, naphthenic, or mixed paraffinic-naphthenic. Oils derived from coal or shale are also useful in the present disclosure. Natural oils vary also as to the method used for their production and purification, for example, their distillation range and whether they are straight run or cracked, hydrorefined, or solvent extracted.

Group II and/or Group III hydroprocessed or hydrocracked base stocks, as well as synthetic oils such as polyalphaolefins, alkyl aromatics and synthetic esters, i.e. Group IV and Group V oils are also well known base stock oils.

Synthetic oils include hydrocarbon oil such as polymerized and interpolymerized olefins (polybutylenes, polypropylenes, propylene isobutylene copolymers, ethylene-olefin copolymers, and ethylene-alphaolefin copolymers, for example). Polyalphaolefin (PAO) oil base stocks, the Group IV API base stocks, are commonly used synthetic hydrocarbon oil. By way of example, PAOs derived from C₂-C₁₆ olefins or mixtures thereof may be utilized. See U.S. Pat. Nos. 4,956,122; 4,827,064; and 4,827,073, which are incorporated herein by reference in their entirety. Group IV oils, that is, the PAO base stocks have viscosity indices preferably greater than 130, more preferably greater than 135, still more preferably greater than 140.

Metallocene catalyzed polyalphaolefins (mPAOs) can be prepared from metallocene or other single-site catalysts. The olefin can be from C₂-C₁₈, or combinations of any alpha-olefins.

Oligomerization/polymerization using a metallocene catalyst can be carried out under the conditions appropriate to the selected alpha-olefin feed and metallocene catalyst. An illustrative metallocene-catalyzed alpha-olefin oligomerization/polymerization process is described in WO 2007/011973, which is incorporated herein by reference in its entirety and to which reference is made for details of feeds, metallocene catalysts, process conditions and characterizations of products.

Esters in a minor amount may be useful in the lubricating oils of this disclosure. The presence or absence of these additional components does not adversely affect the compositions of this disclosure. Additive solvency and seal compatibility characteristics may be secured by the use of esters such as the esters of dibasic acids with monoalkanols and the polyol esters of monocarboxylic acids. Esters of the former type include, for example, the esters of dicarboxylic acids such as phthalic acid, succinic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acid, alkenyl malonic acid, etc., with a variety of alcohols such as butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, etc. Specific examples of these types of esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, etc.

Particularly useful synthetic esters are those which are obtained by reacting one or more polyhydric alcohols, preferably the hindered polyols such as the neopentyl polyols; e.g., neopentyl glycol, trimethylol ethane, 2-methyl-2-propyl-1,3-propanediol, trimethylol propane, pentaerythritol and dipentaerythritol with alkanoic acids containing at least 4 carbon atoms, preferably C₅ to C₃₀ acids such as saturated straight chain fatty acids including caprylic acid, capric acids, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, and behenic acid, or the corresponding branched chain fatty acids or unsaturated fatty acids such as oleic acid, or mixtures of any of these materials.

Esters should be used in a amount such that the improved wear and corrosion resistance provided by the lubricating oils of this disclosure are not adversely affected. The esters preferably have a ASTM D5293 viscosity of less than 10,000 cP at −35° C.

Non-conventional or unconventional base stocks and/or base oils include one or a mixture of base stock(s) and/or base oil(s) derived from: (1) one or more Gas-to-Liquids (GTL) materials, as well as (2) hydrodewaxed, or hydroisomerized/catalytic (and/or solvent) dewaxed base stock(s) and/or base oils derived from synthetic wax, natural wax or waxy feeds, mineral and/or non-mineral oil waxy feed stocks such as gas oils, slack waxes (derived from the solvent dewaxing of natural oils, mineral oils or synthetic oils; e.g., Fischer-Tropsch feed stocks), natural waxes, and waxy stocks such as gas oils, waxy fuels hydrocracker bottoms, waxy raffinate, hydrocrackate, thermal crackates, foots oil or other mineral, mineral oil, or even non-petroleum oil derived waxy materials such as waxy materials recovered from coal liquefaction or shale oil, linear or branched hydrocarbyl compounds with carbon number of 20 or greater, preferably 30 or greater and mixtures of such base stocks and/or base oils.

GTL materials are materials that are derived via one or more synthesis, combination, transformation, rearrangement, and/or degradation/deconstructive processes from gaseous carbon-containing compounds, hydrogen-containing compounds and/or elements as feed stocks such as hydrogen, carbon dioxide, carbon monoxide, water, methane, ethane, ethylene, acetylene, propane, propylene, propyne, butane, butylenes, and butynes. GTL base stocks and/or base oils are GTL materials of lubricating viscosity that are generally derived from hydrocarbons; for example, waxy synthesized hydrocarbons, that are themselves derived from simpler gaseous carbon-containing compounds, hydrogen-containing compounds and/or elements as feed stocks. GTL base stock(s) and/or base oil(s) include oils boiling in the lube oil boiling range (1) separated/fractionated from synthesized GTL materials such as, for example, by distillation and subsequently subjected to a final wax processing step which involves either or both of a catalytic dewaxing process, or a solvent dewaxing process, to produce lube oils of reduced/low pour point; (2) synthesized wax isomerates, comprising, for example, hydrodewaxed or hydroisomerized cat and/or solvent dewaxed synthesized wax or waxy hydrocarbons; (3) hydrodewaxed or hydroisomerized cat and/or solvent dewaxed Fischer-Tropsch (F-T) material (i.e., hydrocarbons, waxy hydrocarbons, waxes and possible analogous oxygenates); preferably hydrodewaxed or hydroisomerized/followed by cat and/or solvent dewaxing dewaxed F-T waxy hydrocarbons, or hydrodewaxed or hydroisomerized/followed by cat (or solvent) dewaxing dewaxed, F-T waxes, or mixtures thereof.

GTL base stock(s) and/or base oil(s) derived from GTL materials, especially, hydrodewaxed or hydroisomerized/followed by cat and/or solvent dewaxed wax or waxy feed, preferably F-T material derived base stock(s) and/or base oil(s), are characterized typically as having kinematic viscosities at 100° C. of from 2 mm²/s to 50 mm²/s (ASTM D445). They are further characterized typically as having pour points of −5° C. to −40° C. or lower (ASTM D97). They are also characterized typically as having viscosity indices of 80 to 140 or greater (ASTM D2270).

In addition, the GTL base stock(s) and/or base oil(s) are typically highly paraffinic (>90% saturates), and may contain mixtures of monocycloparaffins and multicycloparaffins in combination with non-cyclic isoparaffins. The ratio of the naphthenic (i.e., cycloparaffin) content in such combinations varies with the catalyst and temperature used. Further, GTL base stock(s) and/or base oil(s) typically have very low sulfur and nitrogen content, generally containing less than 10 ppm, and more typically less than 5 ppm of each of these elements. The sulfur and nitrogen content of GTL base stock(s) and/or base oil(s) obtained from F-T material, especially F-T wax, is essentially nil. In addition, the absence of phosphorous and aromatics make this materially especially suitable for the formulation of low sulfur, sulfated ash, and phosphorus (low SAP) products.

The term GTL base stock and/or base oil and/or wax isomerate base stock and/or base oil is to be understood as embracing individual fractions of such materials of wide viscosity range as recovered in the production process, mixtures of two or more of such fractions, as well as mixtures of one or two or more low viscosity fractions with one, two or more higher viscosity fractions to produce a blend wherein the blend exhibits a target kinematic viscosity.

The GTL material, from which the GTL base stock(s) and/or base oil(s) is/are derived is preferably an F-T material (i.e., hydrocarbons, waxy hydrocarbons, wax).

Base oils for use in the formulated lubricating oils useful in the present disclosure are any of the variety of oils corresponding to API Group I, Group II, Group III, Group IV, and Group V oils and mixtures thereof, preferably API Group II, Group III, Group IV, and Group V oils and mixtures thereof, more preferably the Group III to Group V base oils due to their exceptional volatility, stability, viscometric and cleanliness features. Minor quantities of Group I stock, such as the amount used to dilute additives for blending into formulated lube oil products, can be tolerated but should be kept to a minimum, i.e. amounts only associated with their use as diluent/carrier oil for additives used on an “as-received” basis. Even in regard to the Group II stocks, it is preferred that the Group II stock be in the higher quality range associated with that stock, i.e. a Group II stock having a viscosity index in the range 100<VI<120.

In addition, the GTL base stock(s) and/or base oil(s) are typically highly paraffinic (>90% saturates), and may contain mixtures of monocycloparaffins and multicycloparaffins in combination with non-cyclic isoparaffins. The ratio of the naphthenic (i.e., cycloparaffin) content in such combinations varies with the catalyst and temperature used. Further, GTL base stock(s) and/or base oil(s) and hydrodewaxed, or hydroisomerized/cat (and/or solvent) dewaxed base stock(s) and/or base oil(s) typically have very low sulfur and nitrogen content, generally containing less than 10 ppm, and more typically less than 5 ppm of each of these elements. The sulfur and nitrogen content of GTL base stock(s) and/or base oil(s) obtained from F-T material, especially F-T wax, is essentially nil. In addition, the absence of phosphorous and aromatics make this material especially suitable for the formulation of low sulfur, sulfated ash, and phosphorus (low SAP) products.

Alkylated aromatic base stock components useful in this disclosure include, for example, alkylated naphthalenes and alkylated benzenes. The alkylated aromatic base stock can be any hydrocarbyl molecule that contains at least 5% of its weight derived from an aromatic moiety such as a benzenoid moiety or naphthenoid moiety, or their derivatives. These alkylated aromatic base stocks include alkyl benzenes, alkyl naphthalenes, alkyl diphenyl oxides, alkyl naphthols, alkyl diphenyl sulfides, alkylated bis-phenol A, alkylated thiodiphenol, and the like. The alkylated aromatic base stock can be mono-alkylated, dialkylated, polyalkylated, and the like. The aromatic can be mono- or poly-functionalized. The hydrocarbyl groups can range from C₆ up to C₆₀ with a range of C₈ to C₄₀ often being preferred. A mixture of hydrocarbyl groups is often preferred. The hydrocarbyl group can optionally contain sulfur, oxygen, and/or nitrogen containing substituents. The aromatic group can also be derived from natural (petroleum) sources, provided at least 5% of the molecule is comprised of an above-type aromatic moiety. Viscosities at 100° C. of approximately 3 cSt to 50 cSt are preferred, with viscosities of approximately 3.4 cSt to 20 cSt often being more preferred for the alkylated aromatic base stock. Naphthalene or methyl naphthalene, for example, can be alkylated with olefins such as octene, decene, dodecene, tetradecene or higher, mixtures of similar olefins, and the like.

Illustrative alkylated naphthalenes useful in the present disclosure are described, for example, in U.S. Patent Publication No. 2008/0300157.

Examples of typical alkyl naphthalenes are mono-, di-, tri-, tetra-, or penta-C₃ alkyl naphthalene, C₄ alkyl naphthalene, C₅ alkylnaphthalene, C₆ alkyl naphthalene, Cs alkyl naphthalene, C₁₀ alkyl naphthalene, C₁₋₂ alkyl naphthalene, C₁₋₄ alkyl naphthalene, C₁₋₆ alkyl naphthalene, C₁₋₈ alkyl naphthalene, etc., C₁₀-C₁₄ mixed alkyl naphthalene, C₆-C₁₈ mixed alkyl naphthalene, or the mono-, di-, tri-, tetra-, or penta C₃, C₄, C₅, C₆, C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈ or mixture thereof alkyl monomethyl, dimethyl, ethyl, diethyl, or methylethyl naphthalene, or mixtures thereof. The alkyl group can also be branched alkyl group with C₁₀-C₃₀₀, e.g., C₂₄-C₅₆ branched alkyl naphthalene, C₂₄-C₅₆ branched alkyl mono-, di-, tri-, tetra- or penta-C₁-C₄ naphthalene. These branched alkyl group substituted naphthalenes or branched alkyl group substituted mono-, di-, tri-, tetra- or penta C₁-C₄ naphthalene can also be used as mixtures with the previously recited materials. These branched alkyl group can be prepared from oligomerization of small olefins, such as C₅-C₂₄ alpha- or internal-olefins. When the branched alkyl group is very large (that is 8 to 300 carbons), usually only one or two of such alkyl groups are attached to the naphthalene core. The alkyl groups on the naphthalene ring can also be mixtures of the above alkyl groups. Sometimes mixed alkyl groups are advantageous because they provide more improvement of pour points and low temperature fluid properties. The fully hydrogenated fluid alkylnaphthalenes can also be used for blending with GTL base stock/base oil, but the alkyl naphthalenes are preferred.

Typically the alkyl naphthalenes are prepared by alkylation of naphthalene or short chain alkyl naphthalene, such as methyl or di-methyl naphthalene, with olefins, alcohols or alkylchlorides of 6 to 24 carbons over acidic catalyst inducing typical Friedel-Crafts catalysts. Typical Friedel-Crafts catalysts are AlCl₃, BF₃, HT, zeolites, amorphous alumniosilicates, acid clays, acidic metal oxides or metal salts, USY, etc.

Methods for the production of alkylnaphthalenes suitable for use in the present disclosure are described in U.S. Pat. Nos. 5,034,563, 5,516,954, and 6,436,882, as well as in references cited in those patents as well as taught elsewhere in the literature. Because alkylated naphthalene synthesis techniques are well known to those skilled in the art as well as being well documented in the literature such techniques will not be further addressed herein.

The naphthalene or mono- or di-substituted short chain alkyl naphthalenes can be derived from any conventional naphthalene-producing process from petroleum, petrochemical process or coal process or source stream. Naphthalene-containing feeds can be made from aromaticization of suitable streams available from the F-T process. For example, aromatization of olefins or paraffins can produce naphthalene or naphthalene-containing component. Many medium or light cycle oils from petroleum refining processes contain significant amounts of naphthalene, substituted naphthalenes or naphthalene derivatives. Indeed, substituted naphthalenes recovered from whatever source, if possessing up to three alkyl carbons can be used as raw material to produce alkylnaphthalene for this disclosure. Furthermore, alkylated naphtahlenes recovered from whatever source or processing can be used in the present method, provided they possess kinematic viscosities, VI, pour point, etc.

Suitable alkylated naphthalenes are available commercially from ExxonMobil under the tradename Synesstic AN or from King Industries under the tradename NA-Lube naphthalene-containing fluids.

Illustrative alkylated benzenes useful in this disclosure include, for example, those described in U.S. Patent Publication 2008/0300157. Alkylated benzenes having a viscosity at 100° C. of 1.5 to 600 cS, VI of 0 to 200 and pour point of 0° C. or less, preferably −15° C. or less, more preferably −25° C. or less, still more preferably −35° C. or less, most preferably −60° C. or less are useful for this disclosure.

Illustrative monoalkylated benzenes include, for example, linear C₁₀-C₃₀ alkyl benzene or a C₁₀-C₃₀₀ branched alkyl benzene, preferably C₁₀-C₁₀₀ branched alkyl benene, more preferably C₁₅-C₅₀ branched alkyl group. Illustrative miltialkylated benzenes include, for example, those in which one or two of the alkyl groups can be small alkyl radical of C₁-C₅ alkyl group, preferably C₁-C₂ alkyl group. The other alkyl group or groups can be any combination of linear C₁₀-C₃₀ alkyl group, or branched Cm and higher up to C₃₀₀ alkyl group, preferably C₁₅-C₅₀ branched alkyl group. These branched large alkyl radicals can be prepared from the oligomerization or polymerization of C₃-C₂₀, internal or alpha-olefins or mixture of these olefins. The total number of carbons in the alkyl substituents ranged from C₁₀-C₃₀₀. Preferred alkyl benzene fluids can be prepared according to U.S. Pat. Nos. 6,071,864 and 6,491,809.

Included in this class of base stock blend components are, for example, long chain alkylbenzenes and long chain alkyl naphthalenes which are preferred materials since they are hydrolytically stable and may therefore be used in combination with the PAO component of the base stock in wet applications. The alkylnaphthalenes are known materials and are described, for example, in U.S. Pat. No. 4,714,794. The use of a mixture of monoalkylated and polyalkylated naphthalene as a base for synthetic functional fluids is also described in U.S. Pat. No. 4,604,491. The preferred alkylnaphthalenes are those having a relatively long chain alkyl group typically from 10 to 40 carbon atoms although longer chains may be used if desired. Alkylnaphthalenes produced by alkylating naphthalene with an olefin of 14 to 20 carbon atoms has particularly good properties, especially when zeolites such as the large pore size zeolites are used as the alkylating catalyst, as described in U.S. Pat. No. 5,602,086. These alkylnaphthalenes are predominantly monosubstituted naphthalenes with attachment of the alkyl group taking place predominantly at the 1- or 2-position of the alkyl chain. The presence of the long chain alkyl groups confers good viscometric properties on the alkyl naphthalenes, especially when used in combination with the PAO components which are themselves materials of high viscosity index, low pour point and good fluidity.

An alternative secondary blending stock is an alkylbenzene or mixture of alkylbenzenes. The alkyl substituents in these fluids are typically alkyl groups of 8 to 25 carbon atoms, usually from 10 to 18 carbon atoms and up to three such substituents may be present, as described in ACS Petroleum Chemistry Preprint 1053-1058, “Poly n-Alkylbenzene Compounds: A Class of Thermally Stable and Wide Liquid Range Fluids”, Eapen et al, Phila. 1984. Tri-alkyl benzenes may also be produced by the cydodimerization of 1-alkynes of 8 to 12 carbon atoms as described in U.S. Pat. No. 5,055,626. Other alkylbenzenes are described in U.S. Pat. No. 4,658,072. Alkylbenzenes have been used as lubricant base stocks, especially for low temperature applications. They are commercially available from producers of linear alkylbenzenes (LABs) such as Vista Chemical Co, Huntsman Chemical Co. as well as ChevronTexaco and Nippon Oil Co. The linear alkylbenzenes typically have good low pour points and low temperature viscosities and VI values greater than 100 together with good solvency for additives. Other alkylated aromatics which may be used when desirable are described, for example, in “Synthetic Lubricants and High Performance Functional Fluids”, Dressler, H., chap 5, (R. L. Shubkin (Ed.)), Marcel Dekker, New York 1993.

Also included in this class and with very desirable lubricating characteristics are the alkylated aromatic compounds including the alkylated diphenyl compounds such as the alkylated diphenyl oxides, alkylated diphenyl sulfides and alkylated diphenyl methanes and the alkylated phenoxathins as well as the alkylthiophenes, alkyl benzofurans and the ethers of sulfur-containing aromatics. Lubricant blend components of this type are described, for example, in U.S. Pat. Nos. 5,552,071; 5,171,195; 5,395,538; 5,344,578; and 5,371,248.

The alkylated aromatic base stock component is typically used in an amount from 1% to 15%, preferably 2% to 10%, and more preferably 4% to 8%, depending on the application.

In an embodiment, the at least two base stocks have a difference in surface tension sufficient to provide enhanced foaming of the lubricating oil. FIG. 2 graphically depicts the difference in surface tension (in dynes/cm) versus LOAST volume increase at 25% treat rate of a 6 cSt blend stock. As shown in FIG. 2, maximizing the difference in surface tension of the at least two base stocks enhances foaming of the lubricating oil. FIG. 6 shows that measurable enhanced foam begins at a surface tension difference of approximately 1.0 dynes/cm and is proportional to the difference in surface tension.

In the lubricating oils of this disclosure, the at least two base stocks have a difference in surface tension of greater than 1.0 dynes/cm, preferably greater than 2.0 dynes/cm, and more preferably greater than 3.0 dynes/cm. The measurable enhanced foam increases with increasing surface tension between the at least two base stocks.

Preferably, the at least two base stocks are selected from poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO) base stocks such that one or more of foam tendency and foam stability are improved as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

Preferably, the at least two base stocks comprise a poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO). The at least two base stocks can comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities and different chain length olefin feedstocks. The at least two base stocks can comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities, and the first mPAO comprises C₂-C₁₆ feedstocks and the second mPAO comprises a different ratio of C₂-C₁₆ feedstocks.

The at least two base stocks are mixed in a ratio such that one or more of foam tendency and foam stability are improved as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

The mixture of base stock components of the present lubricating oils can vary over a wide range. The mixtures can comprise from 5 weight percent to 95 weight percent, preferably from 20 weight percent to 80 weight percent, and more preferably from 40 weight percent to 60 weight percent, of a first base stock and from 5 weight percent to 95 weight percent, preferably from 20 weight percent to 80 weight percent, and more preferably from 40 weight percent to 60 weight percent, of a second base stock, based on the total weight of the lubricating oil.

Other Additives

The formulated lubricating oil useful in the present disclosure may additionally contain one or more of the other commonly used lubricating oil performance additives including but not limited to dispersants, other detergents, corrosion inhibitors, rust inhibitors, metal deactivators, other anti-wear agents and/or extreme pressure additives, anti-seizure agents, wax modifiers, viscosity index improvers, viscosity modifiers, fluid-loss additives, seal compatibility agents, other friction modifiers, lubricity agents, anti-staining agents, chromophoric agents, demulsifiers, emulsifiers, densifiers, wetting agents, gelling agents, tackiness agents, colorants, antioxidants or oxidation inhibitors, and others. For a review of many commonly used additives, see Klamann in Lubricants and Related Products, Verlag Chemie, Deerfield Beach, Fla.; ISBN 0-89573-177-0. Reference is also made to “Lubricant Additives” by M. W. Ranney, published by Noyes Data Corporation of Parkridge, N.J. (1973) and “Lubricant Additives: Chemistry and Applications” edited by L. R. Rudnick, published by CRC Press of Boca Raton, Fla. (2009).

The types and quantities of performance additives used in combination with the instant disclosure in lubricant compositions are not limited by the examples shown herein as illustrations. The presence or absence of these lubricating oil performance additives does not adversely affect the compositions of this disclosure.

Non-limiting exemplary ranges for the components in the lubricant compositions disclosed herein are given in the table below wherein * in the table signifies that at least two base polyalphaolefins (polyalphaolefin-A and polyalphaolefin-B) have a difference in surface tension of greater than about 1.0 dynes/cm, preferably greater than about 2.0 dynes/cm, and more preferably greater than about 3.0 dynes/cm. The additives in the lubricant compositions disclosed herein are discussed in detail below.

More Range Preferably Preferably  15-1000  15-1000  15-1000 ISO VG 5-95  5-95  10-90 Polyalphaolefin-A* 5-95  5-95  10-90 Polyalphaolefin-B* 0-70  0-70  10-25 Alkylated Aromatic or Ester 0-10  0-5   0-2.5 VI Improver/Viscosity Modifier 0-2.0 0.3-2.0  0.3-1.5 Antioxidant 0-0.4 0-0.4 0.06-0.25 Metal Passivator 0-1.0 0-1.0   0-0.45 EP/Antiwear 0-1.0 0-1.0   0-0.45 Rust/Corrosion Inhibitors 0-1.5 0-1.5 0.1-1.0 Profoamant/Defoamant/Demulsifier

Viscosity Improvers

Viscosity improvers (also known as Viscosity Index modifiers, and VI improvers) increase the viscosity of the oil composition at elevated temperatures which increases film thickness, while having limited effect on viscosity at low temperatures.

Suitable viscosity improvers include high molecular weight hydrocarbons, polyesters and viscosity index improver dispersants that function as both a viscosity index improver and a dispersant. Typical molecular weights of these polymers are between 10,000 to 1,000,000, more typically 20,000 to 500,000, and even more typically between 50,000 and 200,000.

Examples of suitable viscosity improvers are polymers and copolymers of methacrylate, butadiene, olefins, or alkylated styrenes. Polyisobutylene is a commonly used viscosity index improver. Another suitable viscosity index improver is polymethacrylate (copolymers of various chain length alkyl methacrylates, for example), some formulations of which also serve as pour point depressants. Other suitable viscosity index improvers include copolymers of ethylene and propylene, hydrogenated block copolymers of styrene and isoprene, and polyacrylates (copolymers of various chain length acrylates, for example). Specific examples include styrene-isoprene or styrene-butadiene based polymers of 50,000 to 200,000 molecular weight.

The amount of viscosity modifier may range from zero to 8 wt %, preferably zero to 4 wt %, more preferably zero to 2 wt % based on active ingredient and depending on the specific viscosity modifier used.

Antioxidants

Typical anti-oxidant include phenolic anti-oxidants, aminic anti-oxidants and oil-soluble copper complexes.

The phenolic antioxidants include sulfurized and non-sulfurized phenolic antioxidants. The terms “phenolic type” or “phenolic antioxidant” used herein includes compounds having one or more than one hydroxyl group bound to an aromatic ring which may itself be mononuclear, e.g., benzyl, or poly-nuclear, e.g., naphthyl and spiro aromatic compounds. Thus “phenol type” includes phenol per se, catechol, resorcinol, hydroquinone, naphthol, etc., as well as alkyl or alkenyl and sulfurized alkyl or alkenyl derivatives thereof, and bisphenol type compounds including such bi-phenol compounds linked by alkylene bridges sulfuric bridges or oxygen bridges. Alkyl phenols include mono- and poly-alkyl or alkenyl phenols, the alkyl or alkenyl group containing from 3-100 carbons, preferably 4 to 50 carbons and sulfurized derivatives thereof, the number of alkyl or alkenyl groups present in the aromatic ring ranging from 1 to up to the available unsatisfied valences of the aromatic ring remaining after counting the number of hydroxyl groups bound to the aromatic ring.

Generally, therefore, the phenolic anti-oxidant may be represented by the general formula:

(R)_(x)—Ar—(OH)_(y)

where Ar is selected from the group consisting of:

wherein R is a C₃-C₁₀₀ alkyl or alkenyl group, a sulfur substituted alkyl or alkenyl group, preferably a C₄-C₅₀ alkyl or alkenyl group or sulfur substituted alkyl or alkenyl group, more preferably C₃-C₁₀₀ alkyl or sulfur substituted alkyl group, most preferably a C₄-C₅₀ alkyl group, R^(g) is a C₁-C₁₀₀ alkylene or sulfur substituted alkylene group, preferably a C₂-C₅₀ alkylene or sulfur substituted alkylene group, more preferably a C₂-C₂ alkylene or sulfur substituted alkylene group, y is at least 1 to up to the available valences of Ar, x ranges from 0 to up to the available valances of Ar-y, z ranges from 1 to 10, n ranges from 0 to 20, and m is 0 to 4 and p is 0 or 1, preferably y ranges from 1 to 3, x ranges from 0 to 3, z ranges from 1 to 4 and n ranges from 0 to 5, and p is 0.

Preferred phenolic antioxidant compounds are the hindered phenolics and phenolic esters which contain a sterically hindered hydroxyl group, and these include those derivatives of dihydroxy aryl compounds in which the hydroxyl groups are in the o- or p-position to each other. Typical phenolic antioxidants include the hindered phenols substituted with C₁+ alkyl groups and the alkylene coupled derivatives of these hindered phenols. Examples of phenolic materials of this type 2-t-butyl-4-heptyl phenol; 2-t-butyl-4-octyl phenol; 2-t-butyl-4-dodecyl phenol; 2,6-di-t-butyl-4-heptyl phenol; 2,6-di-t-butyl-4-dodecyl phenol; 2-methyl-6-t-butyl-4-heptyl phenol; 2-methyl-6-t-butyl-4-dodecyl phenol; 2,6-di-t-butyl-4 methyl phenol; 2,6-di-t-butyl-4-ethyl phenol; and 2,6-di-t-butyl 4 alkoxy phenol; and

Phenolic type anti-oxidants are well known in the lubricating industry and commercial examples such as Ethanox® 4710, Irganox® 1076, Irganox® L1035, Irganox® 1010, Irganox® L109, Irganox® L118, Irganox® L135 and the like are familiar to those skilled in the art. The above is presented only by way of exemplification, not limitation on the type of phenolic anti-oxidants which can be used.

The phenolic antioxidant can be employed in an amount in the range of 0.1 to 3 wt %, preferably 0.25 to 2.5 wt %, more preferably 0.5 to 2 wt % on an active ingredient basis.

Aromatic amine antioxidants include phenyl-a-naphthyl amine which is described by the following molecular structure:

wherein R^(z) is hydrogen or a C₁ to C₁₄ linear or C₃ to C₁₄ branched alkyl group, preferably C₁ to C₁₀ linear or C₃ to C₁₀ branched alkyl group, more preferably linear or branched C₆ to C₈ and n is an integer ranging from 1 to 5 preferably 1. A particular example is Irganox L06.

Other aromatic amine antioxidants include other alkylated and non-alkylated aromatic amines such as aromatic monoamines of the formula R⁸R⁹R¹⁰N where R⁸ is an aliphatic, aromatic or substituted aromatic group, R⁹ is an aromatic or a substituted aromatic group, and R¹⁰ is H, alkyl, aryl or R¹¹S(O)xR¹² where R¹¹ is an alkylene, alkenylene, or aralkylene group, R¹² is a higher alkyl group, or an alkenyl, aryl, or alkaryl group, and x is 0, 1 or 2. The aliphatic group R⁸ may contain from 1 to 20 carbon atoms, and preferably contains from 6 to 12 carbon atoms. The aliphatic group is a saturated aliphatic group. Preferably, both R⁸ and R⁹ are aromatic or substituted aromatic groups, and the aromatic group may be a fused ring aromatic group such as naphthyl. Aromatic groups R⁸ and R⁹ may be joined together with other groups such as S.

Typical aromatic amines anti-oxidants have alkyl substituent groups of at least 6 carbon atoms. Examples of aliphatic groups include hexyl, heptyl, octyl, nonyl, and decyl. Generally, the aliphatic groups will not contain more than 14 carbon atoms. The general types of such other additional amine antioxidants which may be present include diphenylamines, phenothiazines, imidodibenzyls and diphenyl phenylene diamines. Mixtures of two or more of such other additional aromatic amines may also be present. Polymeric amine antioxidants can also be used.

Another class of antioxidant used in lubricating oil compositions and which may also be present are oil-soluble copper compounds. Any oil-soluble suitable copper compound may be blended into the lubricating oil. Examples of suitable copper antioxidants include copper dihydrocarbyl thio- or dithio-phosphates and copper salts of carboxylic acid (naturally occurring or synthetic). Other suitable copper salts include copper dithiacarbamates, sulphonates, phenates, and acetylacetonates. Basic, neutral, or acidic copper Cu(I) and or Cu(II) salts derived from alkenyl succinic acids or anhydrides are known to be particularly useful.

Such antioxidants may be used individually or as mixtures of one or more types of antioxidants, the total amount employed being an amount of 0.50 to 5 wt %, preferably 0.75 to 3 wt % (on an as-received basis).

Detergents

In addition to the alkali or alkaline earth metal salicylate detergent which is an optional component in the present disclosure, other detergents may also be present. While such other detergents can be present, it is preferred that the amount employed be such as to not interfere with the synergistic effect attributable to the presence of the salicylate. Therefore, most preferably such other detergents are not employed.

If such additional detergents are present, they can include alkali and alkaline earth metal phenates, sulfonates, carboxylates, phosphonates and mixtures thereof. These supplemental detergents can have total base number (TBN) ranging from neutral to highly overbased, i.e. TBN of 0 to over 500, preferably 2 to 400, more preferably 5 to 300, and they can be present either individually or in combination with each other in an amount in the range of from 0 to 10 wt %, preferably 0.5 to 5 wt % (active ingredient) based on the total weight of the formulated lubricating oil. As previously stated, however, it is preferred that such other detergent not be present in the formulation.

Such additional other detergents include by way of example and not limitation calcium phenates, calcium sulfonates, magnesium phenates, magnesium sulfonates and other related components (including borated detergents).

Sulfur Containing Compounds

Sulfur-containing compounds useful as additives in this disclosure include, for example, alkyl dithio carbamate, dialkyl dimercaptothiadiazole, other sulfur containing metal passivators, and combinations of any of the foregoing.

Dispersants

During engine operation, oil-insoluble oxidation byproducts are produced. Dispersants help keep these byproducts in solution, thus diminishing their deposition on metal surfaces. Dispersants may be ashless or ash-forming in nature. Preferably, the dispersant is ashless. So-called ashless dispersants are organic materials that form substantially no ash upon combustion. For example, non-metal-containing or borated metal-free dispersants are considered ashless. In contrast, metal-containing detergents discussed above form ash upon combustion.

Suitable dispersants typically contain a polar group attached to a relatively high molecular weight hydrocarbon chain. The polar group typically contains at least one element of nitrogen, oxygen, or phosphorus. Typical hydrocarbon chains contain 50 to 400 carbon atoms.

A particularly useful class of dispersants are the alkenylsuccinic derivatives, typically produced by the reaction of a long chain substituted alkenyl succinic compound, usually a substituted succinic anhydride, with a polyhydroxy or polyamino compound. The long chain group constituting the oleophilic portion of the molecule which confers solubility in the oil, is normally a polyisobutylene group. Many examples of this type of dispersant are well known commercially and in the literature. Exemplary U.S. patents describing such dispersants are U.S. Pat. Nos. 3,172,892; 3,2145,707; 3,219,666; 3,316,177; 3,341,542; 3,444,170; 3,454,607; 3,541,012; 3,630,904; 3,632,511; 3,787,374 and 4,234,435. Other types of dispersant are described in U.S. Pat. Nos. 3,036,003; 3,200,107; 3,254,025; 3,275,554; 3,438,757; 3,454,555; 3,565,804; 3,413,347; 3,697,574; 3,725,277; 3,725,480; 3,726,882; 4,454,059; 3,329,658; 3,449,250; 3,519,565; 3,666,730; 3,687,849; 3,702,300; 4,100,082; 5,705,458. A further description of dispersants may be found, for example, in European Patent Application No. 471 071, to which reference is made for this purpose.

Hydrocarbyl-substituted succinic acid compounds are popular dispersants. In particular, succinimide, succinate esters, or succinate ester amides prepared by the reaction of a hydrocarbon-substituted succinic acid compound preferably having at least 50 carbon atoms in the hydrocarbon substituent, with at least one equivalent of an alkylene amine are particularly useful.

Succinimides are formed by the condensation reaction between alkenyl succinic anhydrides and amines. Molar ratios can vary depending on the amine or polyamine. For example, the molar ratio of alkenyl succinic anhydride to TEPA can vary from 1:1 to 5:1.

Succinate esters are formed by the condensation reaction between alkenyl succinic anhydrides and alcohols or polyols. Molar ratios can vary depending on the alcohol or polyol used. For example, the condensation product of an alkenyl succinic anhydride and pentaerythritol is a useful dispersant.

Succinate ester amides are formed by condensation reaction between alkenyl succinic anhydrides and alkanol amines. For example, suitable alkanol amines include ethoxylated polyalkylpolyamines, propoxylated polyalkylpolyamines and polyalkenylpolyamines such as polyethylene polyamines. One example is propoxylated hexamethylenediamine.

The molecular weight of the alkenyl succinic anhydrides will typically range between 800 and 2,500. The above products can be post-reacted with various reagents such as sulfur, oxygen, formaldehyde, carboxylic acids such as oleic acid, and boron compounds such as borate esters or highly borated dispersants. The dispersants can be borated with from 0.1 to 5 moles of boron per mole of dispersant reaction product.

Mannich base dispersants are made from the reaction of alkylphenols, formaldehyde, and amines. Process aids and catalysts, such as oleic acid and sulfonic acids, can also be part of the reaction mixture. Molecular weights of the alkylphenols range from 800 to 2,500 or more.

Typical high molecular weight aliphatic acid modified Mannich condensation products can be prepared from high molecular weight alkyl-substituted hydroxyaromatics or HN(R)₂ group-containing reactants.

Examples of high molecular weight alkyl-substituted hydroxyaromatic compounds are polypropylphenol, polybutylphenol, and other polyalkylphenols. These polyalkylphenols can be obtained by the alkylation, in the presence of an alkylating catalyst, such as BF₃, of phenol with high molecular weight polypropylene, polybutylene, and other polyalkylene compounds to give alkyl substituents on the benzene ring of phenol having an average 600-100,000 molecular weight.

Examples of HN(R)₂ group-containing reactants are alkylene polyamines, principally polyethylene polyamines. Other representative organic compounds containing at least one HN(R)₂ group suitable for use in the preparation of Mannich condensation products are well known and include the mono- and di-amino alkanes and their substituted analogs, e.g., ethylamine and diethanol amine; aromatic diamines, e.g., phenylene diamine, diamino naphthalenes; heterocyclic amines, e.g., morpholine, pyrrole, pyrrolidine, imidazole, imidazolidine, and piperidine; melamine and their substituted analogs.

Examples of alkylene polyamine reactants include ethylenediamine, diethylene triamine, triethylene tetraamine, tetraethylene pentaamine, pentaethylene hexamine, hexaethylene heptaamine, heptaethylene octaamine, octaethylene nonaamine, nonaethylene decamine, and decaethylene undecamine and mixture of such amines having nitrogen contents corresponding to the alkylene polyamines, in the formula H₂N—(Z—NH—)_(n)H, mentioned before, Z is a divalent ethylene and n is 1 to 10 of the foregoing formula. Corresponding propylene polyamines such as propylene diamine and di-, tri-, tetra-, pentapropylene tri-, tetra-, penta- and hexaamines are also suitable reactants. The alkylene polyamines are usually obtained by the reaction of ammonia and dihalo alkanes, such as dichloro alkanes. Thus the alkylene polyamines obtained from the reaction of 2 to 11 moles of ammonia with 1 to 10 moles of dichloroalkanes having 2 to 6 carbon atoms and the chlorines on different carbons are suitable alkylene polyamine reactants.

Aldehyde reactants useful in the preparation of the high molecular products useful in this disclosure include the aliphatic aldehydes such as formaldehyde (also as paraformaldehyde and formalin), acetaldehyde and aldol (β-hydroxybutyraldehyde). Formaldehyde or a formaldehyde-yielding reactant is preferred.

Preferred dispersants include borated and non-borated succinimides, including those derivatives from mono-succinimides, bis-succinimides, and/or mixtures of mono- and bis-succinimides, wherein the hydrocarbyl succinimide is derived from a hydrocarbylene group such as polyisobutylene having a Mn of from 500 to 5000 or more or a mixture of such hydrocarbylene groups. Other preferred dispersants include succinic acid-esters and amides, alkylphenol-polyamine-coupled Mannich adducts, their capped derivatives, and other related components. Such additives may be used in an amount of 0.1 to 20 wt %, preferably 0.1 to 8 wt %, more preferably 1 to 6 wt % (on an as-received basis) based on the weight of the total lubricant.

Pour Point Depressants

Conventional pour point depressants (also known as lube oil flow improvers) may also be present. Pour point depressant may be added to lower the minimum temperature at which the fluid will flow or can be poured. Examples of suitable pour point depressants include alkylated naphthalenes polymethacrylates, polyacrylates, polyarylamides, condensation products of haloparaffin waxes and aromatic compounds, vinyl carboxylate polymers, and terpolymers of dialkylfumarates, vinyl esters of fatty acids and allyl vinyl ethers. Such additives may be used in amount of 0.0 to 0.5 wt %, preferably 0 to 0.3 wt %, more preferably 0.001 to 0.1 wt % on an as-received basis.

Corrosion Inhibitors/Metal Deactivators

Corrosion inhibitors are used to reduce the degradation of metallic parts that are in contact with the lubricating oil composition. Suitable corrosion inhibitors include aryl thiazines, alkyl substituted dimercapto thiodiazoles thiadiazoles and mixtures thereof. Such additives may be used in an amount of 0.01 to 5 wt %, preferably 0.01 to 1.5 wt %, more preferably 0.01 to 0.2 wt %, still more preferably 0.01 to 0.1 wt % (on an as-received basis) based on the total weight of the lubricating oil composition.

Seal Compatibility Additives

Seal compatibility agents help to swell elastomeric seals by causing a chemical reaction in the fluid or physical change in the elastomer. Suitable seal compatibility agents for lubricating oils include organic phosphates, aromatic esters, aromatic hydrocarbons, esters (butylbenzyl phthalate, for example), and polybutenyl succinic anhydride and sulfolane-type seal swell agents such as Lubrizol 730-type seal swell additives. Such additives may be used in an amount of 0.01 to 3 wt %, preferably 0.01 to 2 wt % on an as-received basis.

Corrosion Inhibitors and Antirust Additives

Anti-rust additives (or corrosion inhibitors) are additives that protect lubricated metal surfaces against chemical attack by water or other contaminants. One type of anti-rust additive is a polar compound that wets the metal surface preferentially, protecting it with a film of oil. Another type of anti-rust additive absorbs water by incorporating it in a water-in-oil emulsion so that only the oil touches the surface. Yet another type of anti-rust additive chemically adheres to the metal to produce a non-reactive surface. Examples of suitable additives include zinc dithiophosphates, metal phenolates, basic metal sulfonates, fatty acids and amines. Such additives may be used in an amount of 0.01 to 5 wt %, preferably 0.01 to 1.5 wt % on an as-received basis.

In addition to the ZDDP anti-wear additives which are essential components of the present disclosure, other anti-wear additives can be present, including zinc dithiocarbamates, molybdenum dialkyldithiophosphates, molybdenum dithiocarbamates, other organo molybdenum-nitrogen complexes, sulfurized olefins, etc.

The term “organo molybdenum-nitrogen complexes” embraces the organo molybdenum-nitrogen complexes described in U.S. Pat. 4,889,647. The complexes are reaction products of a fatty oil, dithanolamine and a molybdenum source. Specific chemical structures have not been assigned to the complexes. U.S. Pat. 4,889,647 reports an infrared spectrum for a typical reaction product of that disclosure; the spectrum identifies an ester carbonyl band at 1740 cm⁻¹ and an amide carbonyl band at 1620 cm⁻¹. The fatty oils are glyceryl esters of higher fatty acids containing at least 12 carbon atoms up to 22 carbon atoms or more. The molybdenum source is an oxygen-containing compound such as ammonium molybdates, molybdenum oxides and mixtures.

Other organo molybdenum complexes which can be used in the present disclosure are tri-nuclear molybdenum-sulfur compounds described in EP 1 040 115 and WO 99/31113 and the molybdenum complexes described in U.S. Pat. 4,978,464.

In the above detailed description, the specific embodiments of this disclosure have been described in connection with its preferred embodiments. However, to the extent that the above description is specific to a particular embodiment or a particular use of this disclosure, this is intended to be illustrative only and merely provides a concise description of the exemplary embodiments. Accordingly, the disclosure is not limited to the specific embodiments described above, but rather, the disclosure includes all alternatives, modifications, and equivalents falling within the true scope of the appended claims. Various modifications and variations of this disclosure will be obvious to a worker skilled in the art and it is to be understood that such modifications and variations are to be included within the purview of this application and the spirit and scope of the claims.

The following are examples of the present disclosure and are not to be construed as limiting.

EXAMPLES

The Lubricant Oil-Air Stability Test (LOAST) was used to measure the foam response of multiple base-stock combinations. The LOAST is an internal standardized analytical technique used to measure the foaming response of lubricating oils that has been found to correlate with the ISO 12152 foam test used in many lubricant performance specifications. 550 grams of lubricant was placed within a beaker and submitted to high shear mixing conditions for 5 minutes to generate foam. The height of the foam was measured by ruler at various intervals after cessation of mixing to quantify the foam tendency and stability. For purposes of this disclosure, foam tendency is defined as the % volume increase of the lubricant 20 seconds after cessation of mixing, and foam stability is defined as the % volume increase remaining after 30 minutes. The LOAST has a measured repeatability of approximately +/−5%.

Mixtures of two similar high viscosity basestocks (PAO-A and PAO-B) produced high foam tendency in the ISO 12152 as shown in FIG. 1. It can be seen from the left side of the plot that neat PAO-B had a 20% volume increase in the ISO 12152 after 20 seconds. On the right side of the plot, neat PAO-A had a 12% volume increase. However, when the two low-foaming base stocks were mixed in a ratio of approximately 4:1 (PAO-B: PAO-A), the ISO 12152 foam tendency increased to 34%—almost twice that of neat PAO-A and almost three times that of neat PAO-B.

A model was developed for predicting the amount of foam that can be generated. As described herein, it is important to maximize the difference in surface tension between the two base stocks as shown in FIG. 2 to enhance the foaming of the mixture. The data generated for FIG. 2 used a combination of 25% of a ˜6 cSt KV100 base stock (Group II, Group III, PAO-C, PAO-D or

PAO-E, Group V) with 75% of a high viscosity PAO (PAO-A or PAO-B). All of these samples had approximately the same viscosity at the test temperature so that viscosity effects were eliminated. Foam was measured using the LOAST test but could be repeated with other test (e.g., ISO 12152) if desired. FIG. 2 shows that measurable enhanced foam began at a surface tension difference of approximately 1.5 dynes/cm and was proportional to the difference in surface tension. By this method it can be clearly shown that PAO-E in PAO-A provides the lowest foaming combination while Grp V in PAO-A shows the highest foaming tendancy. Intermediate differences in surface tension can be used to predict the resulting foam performance of the blends.

The disclosed method does rely on choosing the appropriate concentration of the different basestocks to ensure that peak foam performance is identified when achieving a high foam performing mixture. FIG. 3 shows that as the concentration of Group V alkylated aromatic is increased in PAO-A (difference of 3 dynes/cm), the maximum in foaming potential is identified at approximately 50 wt. %. However, when working towards a low foaming mixture this is less important as the basestocks with similar viscosities are low-foaming at all concentrations. This is evident in the mixture of PAO-B with the Group V alkylated aromatic (difference of 0.8 dynes/cm) which is consistently low-foaming.

The disclosed method is also easily extendable to lubricants with more than 2 different basestocks. FIG. 4 shows 3-component compositions which contain 2 different PAO's and and a PAG co-basestock. The high foam formulation on the left had unsatisfactory foam stability in the D892. However, when examining the basestocks, it is clear that the large surface tension difference between PAO-E and PAO-B (2.4 dynes/cm) is not conducive to a low foaming mixture. Therefore, a low foam formulation was developed using the disclosed method by increasing the concentration of the PAG from 3% to 15%. The difference in surface tension between the PAG and PAO-B is 1.1 dynes/cm, which as described in this method is capable of providing much lower foam performance. This improvement can be seen as the Seq. 1 foam stability is reduced by 63% and the Seq. 3 foam stability is reduced by 93%.

PCT and EP Clauses

1. A method for controlling one or more of foam tendency and foam stability in a lubricating oil comprising providing as the lubricating oil a mixture of at least two base stocks; wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

2. The method of clause 1 wherein the lubricating oil base stock comprises a Group I, II, III, IV or V base oil stock.

3. The method of clauses 1 or 2 wherein the mixture comprises from 5 weight percent to 95 weight percent of a first base stock and from 5 weight percent to 95 weight percent of a second base stock, based on the total weight of the lubricating oil.

4. The method of clauses 1-3 wherein the at least two base stocks are selected from poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO) base stocks such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

5. The method of clauses 1-4 wherein the at least two base stocks are mixed in a ratio such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

6. The method of clauses 1-5 wherein the at least two base stocks comprise a poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO), and wherein the at least two base stocks have a surface tension difference between them of greater than 2.0 dynes/cm.

7. The method of clauses 1-6 wherein the at least two base stocks comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities and different chain length olefin feedstocks.

8. A lubricating oil comprising a mixture of at least two base stocks, wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

9. The lubricating oil of clause 8 wherein the lubricating oil base stock comprises a Group I, II, III, IV or V base oil stock.

10. The lubricating oil of clauses 8 or 9 wherein the mixture comprises from 5 weight percent to 95 weight percent of a first base stock and from 5 weight percent to 95 weight percent of a second base stock, based on the total weight of the lubricating oil.

11. The lubricating oil of clauses 8-10 wherein the at least two base stocks are selected from poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO) base stocks such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

12. The lubricating oil of clauses 8-11 wherein the at least two base stocks are mixed in a ratio such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.

13. The lubricating oil of clauses 8-12 wherein the at least two base stocks comprise a poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO), and wherein the at least two base stocks have a surface tension difference between them of greater than 2.0 dynes/cm.

14. The lubricating oil of clauses 8-13 wherein the at least two base stocks comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities and different chain length olefin feedstocks.

15. The lubricating oil of clauses 8-14 wherein the lubricating oil further comprises one or more of a viscosity improver, antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, inhibitor, and anti-rust additive.

All patents and patent applications, test procedures (such as ASTM methods, UL methods, and the like), and other documents cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent with this disclosure and for all jurisdictions in which such incorporation is permitted.

When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. While the illustrative embodiments of the disclosure have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present disclosure, including all features which would be treated as equivalents thereof by those skilled in the art to which the disclosure pertains.

The present disclosure has been described above with reference to numerous embodiments and specific examples. Many variations will suggest themselves to those skilled in this art in light of the above detailed description. All such obvious variations are within the full intended scope of the appended claims. 

What is claimed is:
 1. A method for controlling one or more of foam tendency and foam stability in a lubricating oil comprising: providing as the lubricating oil a mixture of at least two base stocks; wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.
 2. The method of claim 1 wherein the at least two base stocks are selected from Group I, II, III, IV or V base oil stocks.
 3. The method of claim 1 wherein the at least two base stocks comprise a poly alpha olefin (PAO) or gas-to-liquid (GTL) oil base stock.
 4. The method of claim 1 wherein the mixture comprises from 5 weight percent to 95 weight percent of a first base stock and from 5 weight percent to 95 weight percent of a second base stock, based on the total weight of the lubricating oil.
 5. The method of claim 1 wherein the at least two base stocks are selected from poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO) base stocks such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.
 6. The method of claim 1 wherein the at least two base stocks are mixed in a ratio such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.
 7. The method of claim 1 wherein the at least two base stocks comprise a poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO).
 8. The method of claim 1 wherein the at least two base stocks comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities and different chain length olefin feedstocks.
 9. The method of claim 1 wherein the at least two base stocks have a surface tension difference between them of greater than 2.0 dynes/cm.
 10. The method of claim 1 wherein the lubricating oil further comprises one or more of a viscosity improver, antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, inhibitor, and anti-rust additive.
 11. A lubricating oil comprising a mixture of at least two base stocks, wherein the at least two base stocks have a surface tension difference between them such that, when the surface tension difference is greater than 1.0 dynes/cm, then one or more of foam tendency and foam stability are enhanced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture; and, when the surface tension difference is less than 1.0 dynes/cm, then one or more of foam tendency and foam stability are reduced or equivalent as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.
 12. The lubricating oil of claim 11 wherein the lubricating oil base stock comprises a Group I, II, III, IV or V base oil stock.
 13. The lubricating oil of claim 11 wherein the lubricating oil base stock comprises a poly alpha olefin (PAO) or gas-to-liquid (GTL) oil base stock.
 14. The lubricating oil of claim 11 wherein the mixture comprises from 5 weight percent to 95 weight percent of a first base stock and from 5 weight percent to 95 weight percent of a second base stock, based on the total weight of the lubricating oil.
 15. The lubricating oil of claim 11 wherein the at least two base stocks are selected from poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO) base stocks such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.
 16. The lubricating oil of claim 11 wherein the at least two base stocks are mixed in a ratio such that one or more of foam tendency and foam stability are enhanced or reduced as compared to foam tendency and foam stability achieved using the base stocks separately and not in the mixture.
 17. The lubricating oil of claim 11 wherein the at least two base stocks comprise a poly alpha olefin (PAO) and a metallocene catalyzed poly alpha olefin (mPAO).
 18. The lubricating oil of claim 11 wherein the at least two base stocks comprise metallocene catalyzed poly alpha olefins (mPAO) having similar viscosities and different chain length olefin feedstocks.
 19. The lubricating oil of claim 11 wherein the at least two base stocks have a surface tension difference between them of greater than 2.0 dynes/cm.
 20. The lubricating oil of claim 11 wherein the lubricating oil further comprises one or more of a viscosity improver, antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, inhibitor, and anti-rust additive. 